None
1. Field of the Invention
The present invention relates generally to power transmission chains and particularly to an improved rocker joint for such chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety.
2. Background of the Invention
Power transmission chains are widely used in the automotive industry and other industrial applications. One type of power transmission chain is referred to as a silent chain. Silent chains utilize links with inverted teeth that are formed to engage the teeth of sprockets. Silent chains are often used in engine timing applications, as well as in the transfer of power from a torque converter to a transmission. They are also used in the transfer case of a four-wheel drive vehicle, and in vehicle transmissions.
Silent chains conventionally comprise an assembly of generally flat links that each form two teeth and define a crotch between the teeth. A silent chain is formed from links that are positioned side by side so that a chain tooth is formed by the teeth of adjacent flat links. The links may be interleaved through the width of a chain so that the links forming a chain tooth alternately extend from the chain tooth in opposite directions along the chain to form adjacent chain teeth. Alternatively, a silent chain may be formed by sets or ranks of links that are positioned alongside of each other so that both teeth of a flat link are aligned with the teeth of an adjacent link. Aligned ranks of inverted teeth links are connected to each other so that adjacent links can rotate with respect to each other at the connection. Examples of known silent chains are found in U.S. Pat. Nos. 4,758,210, 5,419,743 and 5,453,059.
Silent chains may include guide links. The guide links are positioned at opposite sides of the chain across its width. The guide links in these locations extend adjacent to the tooth of a sprocket that engages the chain by extending into the chain between chain teeth. The guide link thereby positions the chain on the sprocket. Other silent chains are self-guided. Self-guided chains use inverted tooth outer links having a crotch of a different height than the crotch of the inner links instead of using guide links. The outer links, with a different height crotch between teeth, engages a sprocket having teeth formed to extend into a chain crotch between the outer links to position the chain laterally on the sprocket. An example of a self-guided silent chain is found in U.S. Pat. No. 5,588,926.
For both types of silent chain assemblies, adjacent links may be connected by pivot members that extend through the silent chain through openings in the adjacent flat links at two adjacent chain links that are aligned to collectively form an opening extending across the width of the silent chain. In the past, both pins and rocker joints have been used as the pivot members. Round pins can have a high wear rate due to the sliding action between the pin and the inside of a link opening. To avoid this wear problem, rocker joints have been used.
Conventional rocker joints are formed by two members, a pin and a rocker that extend through the width of a silent chain. The pin engages a chain link extending in one direction along the chain from the rocker joint, and the rocker engages a chain link extending in the opposite direction. The pin and the rocker each form a rocking surface. The pin rocking surface faces generally along the chain direction that the link engaging the pin extends, and the rocker rocking surface faces generally along the chain direction that the link engaging the rocker extends. The rocking surfaces of the pin and link contact each other and rock against each other as the links that engage the pin and rocker rotate with respect to each other. By allowing movement by a rocking contact between the pin and rocker as the chain links rotate, rocker joints reduce the wear of the joint as compared to a pin joint or other sliding joint.
When used with a silent chain, typically one member of the rocker joint is longer. The longer member extends across the width of the chain to engage the laterally outermost links that may be guide links. The longer member engages and moves with the chain link that includes the outermost links. The shorter member of the rocker joint resides between the outer links and engages the link that does not include the outermost links.
The pin and rocker of a conventional rocker joint are straight. Conventional rocker joints do not provide a stiff joint between links. The low stiffness of conventional rocker joints produces noise due to tight strand resonance. Additionally, free play in conventional rocker joints causes wash, or link-to link noise.
Noise created by silent chains is a longstanding problem. Reduction of noise created during operation of silent chains has been the focus of many efforts, including changes in the shape of the chain teeth, varying the chain pitch, and phasing the chain and sprocket relationship. Two such prior attempts to decrease noise are disclosed in U.S. Pat. Nos. 5,419,743 and 5,453,059. Prior efforts have not addressed the noise created by tight strand resonance of a silent chain, and xe2x80x9cwashxe2x80x9d, or link-to link noise caused by free play in a chain.
The prior art discloses rocker joints and other two member chain joints in which one or both members are not straight. U.S. Pat. No. 2,067,243 discloses the use of a toothed drive chain with a pin and spring member in each aperture of the links. The pins are straight and define a flat surface against which a spring member is positioned. The spring member is bent, or cambered, so that the spring contacts the pin near its middle and is separated from the pin near the pin ends. This configuration is referred to as outwardly cambered. The pin and spring do not rotate with respect to each other. The spring is not a working part of the joint, but rather urges links apart to take up free play in the joint and to provide stiffness at the joint. Thus, the joint of this patent is a single pin joint.
U.S. Pat. No. 4,764,158 discloses a power transmission chain with rocker joints formed by two bent rockers. Each rocker forms a rocking surface that contacts the rocking surface of the other rocker. The rockers are outwardly cambered so that they contact near their middle and separate from the adjacent rocker near the ends. The rockers are inserted in openings that are sized so that the rockers are spaced from each other thereby increasing the range of motion of the joint. This design is incompatible with a chain having guide links or other link that maintains the chain""s lateral position.
U.S. Pat. No. 4,911,682 discloses a CVT chain belt with two pins forming a rocker joint. The pins form rocker surfaces. One or both pins are inwardly cambered so that the rocker surfaces of the pins contact each other at the ends of the pins. The pins rotate with the links of the CVT chain belt and are cambered to be retained within the chain during handling and assembly. The pins can move laterally within the chain belt. The pins flatten against each other during operation.
U.S. Pat. No. 2,324,640 discloses a chain having joints that include a bowed leaf spring sandwiched between 2 pinnate sections that have semi-cylindrical exterior bearing surfaces. Chain teeth rotate on the exterior bearing surfaces of the pinnate sections. The spring urges the pinnate sections against the links to shorten the chain pitch. The links rotate about the pinnate sections and thus there is no rocking contact at the joint to avoid wear problems.
There remains a need for a rocker joint for a power transmission chain that will reduce tight strand resonance and the noise associated with it, that will provide the reduced wear of a rocker joint, and that will allow use of guide links or self-guided chain technology to maintain the chain""s lateral position.
A rocker joint according to the present invention joins a first chain link of a power transmission chain to an adjacent second chain link of the chain. The first and second chain links are configured to interleave with each other so a joint portion of the first chain link is positioned adjacent to a joint portion of the second chain link. The first and second chain links define openings in the joint portions that are located so that the openings are aligned when the first and second chain links are interleaved with each other. The openings in the chain links bound a joint opening that extends through the first and second chain links.
A rocker joint according to the present invention includes a pin and a rocker that are positioned within the joint opening. The pin extends through the joint opening and engages the opening in the first chain link so that the pin rotates with the first chain link. The rocker extends through the joint opening and engages the opening in the second chain link so that the rocker rotates with the second chain link. The pin is generally straight and defines a rocking surface within the joint opening. The rocker defines a rocking surface that is adjacent to the pin rocking surface. The rocker extends from a first end to a second end and is inwardly cambered so that the rocker rocking surface contacts the pin rocking surface near the first and second ends of the rocker and is separated from the pin rocking surface between the first and second ends of the rocker. The pin and the rocker may define seating surfaces that engage mating surfaces of the openings in the chain links.
The straight pin and inwardly cambered rocker provide increased stiffness of the joint with a resulting reduction of tight strand resonance, as well as an overall lessening of noise by eliminating free play in the chain. Furthermore, the camber allows the chain to be assembled by providing the smallest width of the rocker joint at its ends, providing a small profile leading end for insertion into the joint opening.
For a more complete understanding of the invention, one should refer to the detailed description of the embodiment and the accompanying drawings, which are not to scale.